摘要:

AbstractFar‐field potentials are produced by neural generators located at a distance from the recording electrodes. These potentials were initially characterized incorrectly as being of positive polarity, widespread distribution, and constant latency; however, recent advances have clearly demonstrated that far‐field potentials may be either positive or negative depending upon the location of the electrodes with respect to the orientation of the dipole generator. Additionally, peak latencies in the far‐field can vary with alterations in body position and the spatial distribution of far‐field potentials, while widespread, is not uniform. Recent studies of far‐field potentials suggest how such waveforms are produced when the symmetry of an action potential, as recorded by distant electrodes, is broken by such factors as differing conductivities of volume conductor compartments, direction of action potential propagation, size differentials in adjoining body segments, or the termination of action potential propagation in excitable tissue. Human, animal, and computer experiments support the preceding generalizations. These new explanations are directly applicable to such far‐field potentials as the short latency somatosensory‐evoked potential. Furthermore, since far‐field potentials can also occur in muscle tissue, one should expect that these generalizations will hold with respect to electromyographic potentials. © 1993 John

ISSN:0148-639X    

DOI:10.1002/mus.880160302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe frequency of the acoustic myographic (AMG) signal was examined during fresh and fatigued isometric contractions of quadriceps and during dynamic contractions of biceps brachii (BB) in healthy subjects. Recordings were obtained from quadriceps over a range of forces between 10% and 100% maximal voluntary contraction prior to, and 15 minutes after, a fatiguing exercise. Recordings from BB were obtained over a range of submaximal forces (0–8.5 kg) during concentric and eccentric contractions. The mean power frequency (MPF) of the AMG signal was analyzed during each of these contractions by fast‐Fourier transform (FFT). The MPF was not significantly different (P>0.05) during fresh and fatigued contractions of quadriceps and increased quadratically with force in both states (r= 0.81, fresh;r= 0.77, fatiqued). During concentric contractions of BB the MPF initially with force, but then decreased at the heavier loads (>5.5 kg). The MPF of eccentric contractions did not significantly (P>0.05) alter with force. The AMG MPF was within a similar low frequency range for both muscles, during different types of contraction, and was unaltered with fatigue. © 1993 John Wiley&Sons,

ISSN:0148-639X    

DOI:10.1002/mus.880160303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe pattern of an abnormal median‐normal sural (AMNS) sensory response is associated with acute and chronic inflammatory demyelinating polyradiculoneuropathy (AIDP and CIDP) and considered unusual in other types of neuropathy, although specificity and sensitivity of this pattern have not been evaluated. We compared sensory responses (patterns and absolute values) in patients with AIDP, CIDP, diabetic polyneuropathy (DP), and motor neuron disease (MND). Using strict criteria, the AMNS pattern occurred more frequently in recent onset AIDP (39%) compared with CIDP (28%), DP (14%–23%), or MND (22%) patients. This pattern was found in 3% of control subjects. The extreme pattern of an absent median‐present sural response occurred only in AIDP and CIDP patients and in no other groups. Abnormalities of both nerves were more common in long‐standing polyneuropathies such as CIDP and DP compared with AIDP or MND. Median nerve amplitudes were reduced significantly in AIDP, CIDP, and DP patients compared with MND patients, whereas sural nerve amplitudes were significantly reduced only in DP and CIDP patients. These findings may reflect early distal nerve involvement particularly in AIDP patients which is highlighted by differences in median and sural nerve recording electrode placement. We conclude that, in the appropriate clinical setting, the AMNS pattern, an absent median‐present sural response pattern, or a reduced median amplitude compared with the sural amplitude supports a diagnosis of a primary demyelinating polyneuropathy. © 1993 John Wiley

ISSN:0148-639X    

DOI:10.1002/mus.880160304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractHeart rate variation due to respiration is a window onto autonomic nervous system function and many measures exist that quantify this variability. Computer‐based simulations of 1‐minute deep‐breathing tests, along with common artifacts, were used to compare the most frequently used measures. We found distinct differences in the performance of the measures. Some measures (e.g., SDRR and MSSD) are strongly influenced by the underlying mean heart rate while others (e.g., Max–Min and SDHR) are not. All of the measures tested, exceptR, were influenced by both shifting mean heart rate and single‐beat anomalies.R, on the other hand, is strongly influenced by test duration and breathing asynchronies. Sensitivity to phenomena unrelated to ANS function can reduce the diagnostic discrimination of these measures. We suggest simple improvements to the measures and discuss how some measures may be theoretically superior to others. © 1993 John Wiley

ISSN:0148-639X    

DOI:10.1002/mus.880160305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDuring sustained muscle contraction, an interval of reduced activity follows an electrical cutaneous stimulus, called the cutaneous silent period (CSP). To evoke a CSP, a single stimulus must be painful. We used single sural nerve stimuli to evoke a CSP in ipsilateral soleus muscle, and studied the relationships between stimulus strength, sensory action potential (SAP) morphology, and subjective experience. Near nerve electrodes were employed to record the sural SAP in order to record activity in slower conducting fibers in addition to Aα fibers. In 6 normal subjects, the stimulus strength required to evoke a CSP ranged from 8 to 10 times threshold intensity. Pain threshold was slightly below that necessary to evoke the CSP. SAP shape changed with stimulus strength; main component amplitude occasionally increased as strength increased beyond 10 times threshold, and slowly conducting late components became more prominent. At stimulus intensities or at less than CSP threshold, components were seen conducting from 15–20 m/s that were not observed at lower intensities. We suggest that activation of sensory axons with conduction velocities in the range of Aδ fibers are necessary to evoke the CSP, and that their potentials can be discerned in the SAP. © 1993 John Wiley&Sons,

ISSN:0148-639X    

DOI:10.1002/mus.880160306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of long‐term (40 min) high frequency stimulation (143 Hz) of sensory‐motor tail nerves was studied in normal and in streptozotocindiabetic rats. The study comprised a 6‐week period, repeating the test at 2‐week intervals. In the initial (prediabetic) study, single experiments showed a mild depression of the peak‐to‐peak ampltiude during high frequency stimulation, which reversed completely during a subsequent rest period. In normal rats, the amplitude depression was unchanged in repeated tests over a 6‐week period. Diabetic rats showed a greater amplitude depression during high frequency stimulation. The difference was statistically significant after 2 weeks, but showed no further change at subsequent tests. The greater decrease in the amplitude in diabetic rats may reflect a depression of the axon membrane function, which may be the functionl correlate to the inhibition of the Na/K ATPase activity in diabetes, described by others. Monitoring of the axon membrane functional capacity may have clinical implications in the control of peripheral neuropathies. © 1993 John W

ISSN:0148-639X    

DOI:10.1002/mus.880160307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMagnetic stimulation of cervical spinal roots was shown to elicit sensory potentials (MESP) which could easily be recorded at the fingers with ring electrodes. The latency of the MESP recorded at digit I was significantly shorter and the amplitude higher than of digits III and V. The latencies were largely independent of stimulus strength. In an attempt to localize the place of depolarization, the latencies of these potentials were compared with the N11 of the SEP (reflecting the arrival in the spinal cord) and with F‐wave latencies and motor evoked potentials (MEP) to abductor pollicis brevis. The MESP latencies showed a very constant difference with the N11, being 0.6 ms faster. The mean difference between F latency and MEP was 1.2 ms. It is concluded that the origin of these MESPs is very near the spinal foramina, possibly in the sensory ganglia. © 1993 John Wiley&Sons, I

ISSN:0148-639X    

DOI:10.1002/mus.880160308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractUltrasonography (US) and computed tomography (CT) were compared in studying the associations between long‐term physical training and quadriceps muscle mass and structure in female athletes and controls, aged 66–85 years. Muscle cross‐sectional area (CSA) measured using US correlated highly with that measured using CT, but the latter technique yielded 30% higher values on average. The echo intensity of the fasciae and bone measured by US correlated positively with the mean radiological density and negatively with the relative proportion of fat obtained from CT. Low intramuscular echo intensity was accompanied by high muscle density and low relative proportion of fat. The athletes had larger quadriceps CSA and more discerned fasciae and connective tissue septa but less fat than the controls. The results indicate that US and CT both are useful methods in comparing muscle mass and structure in elderly trained and untrained women. © 1993 John Wiley&Son

ISSN:0148-639X    

DOI:10.1002/mus.880160309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAn 8‐year‐old girl with demyelinating peripheral neuropathy was observed to get markedly weak coincident with a febrile illness. With return of body temperature to normal over 24 hours, her strength improved back to baseline. Subsequently, we studied the effect of temperature on CMAP amplitude of two motor nerves in the patient and two control subjects. Both temperature, measured orally, was raised by immersing the subjects in hot water and lowered by passive cooling. With increase in temperature to 39.5°C, the CMAP amplitudes were reduced by 80% in the patienťs nerves compared to only 48% in the control nerves. These changes recovered with cooling to 36.9°C. We conclude that demyelinated peripheral nerves are more susceptible to temperature‐induced impulse blocking than healthy nerves and provide the first published evidence of the clinical consequences of this phenomenon in a demyelinating disease other than multiple sclerosis. © 1993 John Wiley&

ISSN:0148-639X    

DOI:10.1002/mus.880160310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractTo enable the quantitative assessment of peripheral nerve structure and function, we determined the normal values for sural nerve hydration structure as measured by magnetic resonance proton imaging, and for neurological function with scores for neuropathic symptoms, signs, and nerve conduction properties. Normal human sural nerves contain 24.8 ± 3.4% water. The structural water content of the nerves did not vary systematically in relation to age, height, gender, sural nerve conduction, neurologic symptoms, or examination deficits. In contrast, the neurological function scores were significantly influenced by age and selectively by height. Both nerve structure and function were stable over a 1‐year interval. Measurement of human sural nerve water content in vivo by magnetic resonance proton imaging, and quantitation of the neurological profile of symptoms, signs, and conduction velocity are useful, noninvasive tools for the investigation of diseases in which changes in nerve structure may be related to alterations in nerve function. © 1993 John Wiley&Sons,

ISSN:0148-639X    

DOI:10.1002/mus.880160311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY